This invention relates to a mechanism for cooling engines, especially engines used in military tanks.
Military tanks are commonly powered by diesel engines having a number of cylinders, e.g., twelve cylinders arranged in two banks of six cylinders per bank. The tanks usually weigh several tons, e.g., between forty and sixty tons. Accordingly, the propulsion engines are required to have large power outputs, e.g., 1,200 horsepower or more. The individual engine cylinders have relatively large diameters and stroke lengths, e.g., approximately four inches.
The above factors result in large engine cooling loads. Commonly, water is used as the engine coolant. However, the heated water must, in turn, be cooled before recirculation through the coolant passages in the engine. To accomplish such cooling of the water, it is common to pass the heated water through radiators. Engine-driven fans are located in aerodynamic alignment with the radiators to draw ambient air through the radiators for effecting a coolant action on the water within the radiator.
Even though the engines may be water-cooled, the ultimate (final) cooling action is accomplished by the fan-induced air flow through the radiators. Relatively large air quantities are required.
One existing military tank is powered by an air-cooled engine, designated as the AVDS-1790. That particular engine is equipped with two large fans located on the engine centerline above the engine cylinders; each cylinder has a large number of external cooling fins on its cylinder head area. The two large fans draw ambient air across the external fins to cool the individual cylinders. Large quantities of air are required.
Military tanks differ from conventional automobiles and trucks in that tank hulls are usually constructed with a minimum number of openings or slots in the hull walls; design efforts are made to protect the human occupants and power plant from enemy projectiles, mines, grenades, etc. The aim is to provide as few openings as possible in the hull-turret envelope, and to make any such openings as small as possible areawise.
The presence of large air-water radiators in military tanks is a disadvantage from the standpoint that such radiators subtract from the armored wall area. Such radiators are also disadvantageous from the standpoint that if the radiators should be pierced by an enemy projectile or fragment, the resultant water leakage out of the radiators will cause failure of the cooling systems and overheating of the associated engines.
The presence of large fans in military tanks is similarly disadvantageous in that the associated air flow openings subtract from the armored wall area. In some cases, ballistic grilles are placed across the air flow openings to intercept enemy projectiles or munition fragments. However, such grilles add to the vehicle weight and cut down on the air flow. It would be desirable to eliminate the need for ballistic grilles, or to at least reduce the required face area of such grilles. In a related sense, it would be desirable to reduce the quantity of air required for engine cooling purposes.
I propose an engine-cooling system that overcomes some of the disadvantages of existing engine cooling systems. In the proposed system pressurized air is directed through closed (confined) passages extending around and over each engine cylinder. Each passage has a series of heat transfer fins therein extending in the direction of air flow, i.e., longitudinally along the passage surface. The fins occupy the full height of each passage, such that none of the air is able to bypass the fins; the air is required to flow through the fin spaces rather than over or around the finned areas.
A principal advantage of my invention is the fact that no chassis-mounted radiators or auxiliary fans are required. Another possible advantage of my invention is achievement of coolant air flow at the expense of a greatly reduced air flow requirement for coolant purposes. In my proposed arrangement the coolant air is caused to flow through passages running through the engine in close proximity to the combustion chambers and exhaust passages; the coolant air experiences a much greater temperature increase than the coolant in conventional engine cooling arrangements.
The relatively large temperature rise in the coolant air stream means that only a relatively small quantity of air is required to achieve a given cooling action (considerably smaller than either air or water cooled systems). Smaller air quantities (mass flow rates) translate into relatively small power expenditures (losses) and small air intake openings in the hull surface.